New site just launched: Video.Xbox.com
Movie purchases will play on Xbox consoles, Windows PCs (Xbox video or Zune app), Windows Phones, Zune devices, and the website (SD-only for now).
All prices are for HD purchases: (no link = must buy from Xbox or Windows apps):
The A-Team (Extended Edition)
Cape Fear (1991)
Grandma's Boy (unrated)
I Love You Beth Cooper